This Is Your Brain on Vitamin D

Vitamin D has been much in vogue of late. Like many micronutrients preceding it, such as vitamin B12 and folic acid, it is touted as a cure for a variety of ills. There are concerns about possibly widespread deficiencies. The list of illnesses possibly caused or worsened by such deficiencies is growing rapidly. Current recommended daily requirements are under review, and are considered by many to be too low. While a certain excess of enthusiasm may be present, it is becoming fairly clear that many people are indeed deficient, especially in climates which are not conducive to year round sunlight exposure. And, older persons may be especially at risk. Studies evaluating the association between vitamin D levels and markers and a variety of neurologic problems have come to publication of late. Three such studies appeared in a single recent issue of Neurology. That three manuscripts appear in a single issue of the journal illustrates the perceived importance of this issue.

The first looks at vitamin D levels, dementia and neuroimaging findings in a group receiving home care services. These were persons living in the Boston area who needed assistance with some self-care domain. Vitamin D status was correlated with MRI. The base cohort was 318 patients, with a mean age of 73.5 years old. 44.3% of the patients had vitamin D insufficiency, with frank deficiency seen in 15%. 76 patients (23.9%) had dementia, of which 41 were diagnosed as Alzheimer's Disease. Vitamin D insufficiency was associated with Alzheimer's Disease (odds ratio 2.9) and all cause dementia (OR 2.6). White matter MRI changes were inversely proportional to vitamin D serum levels. However, changes in the hippocampi did not correlate with vitamin D status. The authors conclude that the findings are consistent with the hypothesis that vitamin D related c ognitive impairment may be mediated by vascular mechanisms.

The second is a post-hoc analysis of patients in a French osteoporosis study cohort, a group of community dwelling women over 75 years old. 752 patients (mean age 80 years old) were stratified into vitamin D deficient (n=129; 17.2%) and not deficient (n=623) cohorts. One measure of global cognitive function was obtained, and a variety of potential confounding factors were ascertained. Vitamin D deficient women had statistically significantly worse cognitive function scores, but there was not a linear relationship between vitamin D levels and scores. The OR for cognitive impairment in vitamin D deficient women was 1.99 after adjustment: They were twice as likely to measure as cognitively impaired. This is a significant difference. The authors so comment, and also comment on differences between their study and previous studies on the basis of analysis methodol ogy (categorical v. continuous variables).

And, the last is a study of men only, evaluated over time, abstracted from another osteoporosis study cohort. Another difference: It was longitudinal in nature, evaluating changes over time, as opposed to the cross-sectional evaluations in the first two studies. The cohort was divided into four quartiles, depending on vitamin D serum levels. 1,604 persons, with an average age of about 74 years old, were studied. And, in contrast to the first two studies, no material differences were found. There was a trend towards cognitive impairment in the lower vitamin D serum level groups, but it was not statistically significant. There were differences in baseline demographics between the deficient and not deficient groups, but the authors did adjust for this, and did not think their conclusion was changed as a result.

Thus, vitamin D status may be associated with cognitive function. The first two studies show a strong association between dementia or cognitive impairment and vitamin D status, with at or over double the risk for women with vitamin D deficiencies. The third study found no relationship between vitamin D levels and cognitive performance or decline in older men. Clearly, there is no simple relationship between vitamin D intake and cognitive function. However, it does appear that a relationship does exist. At present, as vitamin D supplementation up to a certain point is safe, it's probably reasonable to recommend a degree of supplementation for older patients, and perhaps consider it for younger persons as well. That said, the dose and form best used are not yet so apparent.